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To Evaluate Significance of Gamma Index Between the Measurement of 2D Detector Arrays and the Calculated Patient 3D Dose Distribution


S Kim

S Kim*, Y Qiu, P Mavroidis, N Papanikolaou, S Stathakis, University of Texas HSC SA, San Antonio, TX

SU-E-T-212 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:
To evaluate significance of gamma index between the measurement of 2D detector arrays and the calculated patient 3D dose distribution.

Methods:
DMLC (Dynamic Multi-Leaf Collimator) of IMRT (Intensity Modulated Radio Therapy) delivery information recorded in log files during delivery. The Dynalog file includes amongst other, the beam on and off status, segment dose index, and individual leaf positions. In this study, three previous treated IMRT patient plans are selected and delivered using a Varian CLINAC 600 C/D linear accelerator equipped with Millennium 120 MLC. Patient specific measurements were obtained using the PTW OCTAVIUS II system for all individual fields, while simultaneously recording the Dynalog file. Using an in-house Matlab code, the dynalog data are converted to an adapted format of fluence map to Eclipse v8.9 treatment planning system. Using the Dynalog file based fluence maps we are able to calculate the dose for each field and the also to calculate the patient dose distribution. Comparisons of individual fields and of the patient 3D distribution were then performed and the analysis was based on gamma index passing rate for the individual fields, and DVH and dose differences for the patient dose distributions.

Results:
Our study confirms that the measured planar dose for individual fields has a good agreement to the calculated dose using the DMLC Dynalog file fluence maps. Filed by field analysis between detector measured and dynalog file fluence based calculations had 94.2% passing pixels using 3mm/3% criteria.

Conclusion:
Results show that the calculated dose based on Dynalog record is comparable to measured dose on PTW OCTAVIUS II detector. Gamma index values showed the reasonable dosimetric identity between two dose distributions.

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